Fourth Study Conference on BALTEX Scala Cinema Gudhjem

of 35 m/s up to 3 hours. Data on wind during storm surge of
15 October 1955 shows that over the sea wind with velocity
more than 20 m/s can continue up to 36 hours, and with
velocity exceeding 30 m/s for up to 12 hours. These data
also indicate that for a short period wind may be as high as
45 m/s.
Figure 3. Distribution of wind directions over the
Baltic Sea, which corresponds to extreme storm surge
in the Gulf of Finland.
Based on these estimations the following wind distribution
was chosen for the extreme water level simulations. Wind
directions were assigned according to Fig.3. Wind velocity
over the Baltic Sea and the Gulf of Finland was assigned
equal to 25 m/s. To the east of Island Moshnyi wind velocity
was increased up to 35 m/s for 2 hours and up to 45 m/s for
1 hour.
Simulations of extreme water level rise should take into
account possible high mean water level in the Baltic Sea.
Mean annual values in station Kronshtadt for the period
1810-2001 is shown in Fig.4. There is no evident trend in
annual water levels. Therefore, global trend in water level
oscillations was set equal to zero.
Figure 4. Mean annual water levels in Kronshtadt in
1810-2001.
The seasonal water level variations are significant. As it is
noted in Jensen et al. (1998) mean water level in the Baltic
reflects mean water level in the North Sea. Water exchange
through the Danish Straits is the main reason of the seasonal
variations of the Baltic water level. Maximum monthly
mean water level in Kronshtadt in the 20 th century was 77
cm in March 1990. Fig.5 shows time history of water levels
in Kronshtadt in this year. Taking into account that due to
prevailing western winds mean water level in the Eastern
Gulf of Finland is higher than in the Baltic Proper, it is
reasonable to assign 60 cm as mean water level in the Baltic
Sea during extreme storm surge.
- 137 -
Figure 5. Water level in Kronshtadt in 1990.
Results of simulation of storm with the parameters defined
above are shown in Fig.6. As it is seen from this figure
simulated maximum water level rise in St.Petersburg
equals to 606 cm, 520 cm in Kronshtadt and 434 cm in
Staroe Garkolovo, near Leningrad Nuclear Power Station.
This result is in very good agreement with the upper limit
of different statistical evaluations. Namely, 430 cm was
received for Staroe Garkolovo by Hydroproject Institute
(Nudner et al, 1998). Such high water level for
Koporskaya Bay was not expected when the investigation
was started.
Figure 6. Simulated time histories of water levels in
St.Petersburg, Kronshtadt and Koporskaya Bay
during extreme storm surge.
References
Atlas of Wind and Sun Climates of Russia. Ed. by
M.M.Borisenko and V.V.Stadnyuk. A.I.Boeikov’s
Main Geophysical Laboratory. St.Petersburg, 1997 (in
Russian).
Jensen J., Blasi Chr. Changes of synoptic water data in the
South-Western Baltic Sea. Proceedings of Second
<strong>Study</strong> <strong>Conference</strong> on BALTEX, 25-29 May, Juliusruh,
Island of Rugen, Germany, pp.95-96, 1998.
Klevanny K.A., Matveyev V.G., Voltzinger N.E. An
integrated modeling system for coastal area dynamics,
International Journal for Numerical Methods in
Fluids, Vol.19, pp. 181-206, 1994.
Nudner I.S. Analysis of influence of floods and other
hydrometeorological factors on buildings of Leningrad
Nuclear Power Station, Technical Report of
Hydroproject Institute. St.Petersburg, 28p., 1998 (in
Russian).
Semenova N.S. Accuracy of determination of wind speeds
with frequency 1 time in 10000 years, Proceedings of
A.I.Boeikov’s Main Geophysical Laboratory,
St.Petersburg, v.3, 1997 (in Russian).